1. Field of the Invention
The invention relates to the synthesis of bisphenols from monophenols and carbonyl compounds such as aldehydes and ketones using concentrated mineral acids such as hydrochloric acid and/or hydrogen chloride gas as acid catalysts and a mercaptan as cocatalyst, which is fixed by an ion pair bond to a matrix that is insoluble in the reaction medium.
2. Description of the Prior Art
The condensation of phenols and carbonyl compounds to form bisphenols with the use of catalysts such as hydrochloric acid (U.S. Pat. Nos. 3,182,308; 2,191,831) and of sulphur-containing compounds as cocatalysts is known (for example, from U.S. Pat. Nos. 2,468,982; 2,623,908, the use of thioglycolic acid and 3-mercaptopropionic acid; from U.S. Pat. No. 2,775,620, the addition of alkyl mercaptans; from Chemical Abstracts 58, 1403e, the addition of hydrogen sulphide). The known sulphur-containing cocatalysts can in practical operation lead to considerable discolorations of the bisphenols and of subsequent products prepared from them such as, for example, polycarbonates, copolycarbonates, polyesters, copolyesters and epoxy resins, if they are not separated so as to leave no residue by means of appropriate purification steps such as, for example, crystallisation of the bisphenol and washing out of the sulphur compounds. Particularly in the case of bisphenols for which the syntheses require very high concentrations of cocatalysts, the separation of the sulphur-containing components is frequently difficult and is associated with undesirable losses of the required target compound, particularly where there is heat stress, for example, during the working-up process.
In contrast, cocatalysts can easily be completely separated by filtration or centrifugation if they are not added in homogeneous phase but, before addition to the educt mixture, are already bonded by ionic bonds to a matrix which is insoluble in the reaction medium. This form of cocatalyst permits extremely high cocatalyst concentrations to be used without the occurrence of the problems regarding quality described above.
The synthesis of bisphenols using cocatalysts fixed to a resin matrix is described in DE-A 3 619 450 (for example, using aminoalkyl mercaptan units) or in DE-A 3 727 641 (for example, using thiazolidine units); the acid catalyst likewise needed here is also bonded in the form of sulphonic esters to the resin matrix.